Drum brake and electric actuator therefor

ABSTRACT

An actuator for a drum brake comprises a housing ( 1 ), a screw mechanism having at least one screw ( 3, 6 ) and a nut ( 4, 7 ), which screw mechanism ( 2 ) is supported with respect to the housing ( 1 ), and drive means ( 3 ) which are drivingly connected to the screw mechanism for providing a linear movement of at least one of the screw and nut with respect to the housing upon driving the screw mechanism. The screw mechanism comprises two axially aligned screws which have opposite lead angles and two corresponding nuts, said screws each engaging a respective nut, the drive means being connected to both screws or to both nuts.

[0001] The invention is related to an actuator for a drum brake,comprising a housing, a screw mechanism comprising at least one screwand a nut, which screw mechanism is supported with respect to thehousing, and drive means which are drivingly connected to the screwmechanism for providing a linear movement of at least one of the screwand nut with respect to the housing upon driving the screw themechanism.

[0002] Such actuator is known from U.S. Pat. No. 5,310,026. It comprisesa screw which is connected to the actuator housing by means of a thrustbearing. The associated nut is held slidably within the housing, and isdriven linearly by rotating the screw. Upon actuation, a linear force isexerted through the nut and the housing. This housing should thereforebe movable, so as to provide e.g. a balanced braking action in a drumbrake.

[0003] The object of the invention is to provide an improved actuator,in which the housing is not part of the force trajectory. This object isachieved in that the screw mechanism comprises two axially alignedscrews which have opposite lead angles and two corresponding nuts, saidscrews each engaging a respective nut, the drive means being connectedto both screws or to both nuts.

[0004] The actuator according to the invention provides a driving actionthrough the pair of nuts or screws, without exerting loads on thehousing. As a result, the housing can be carried out as a relativelysimple component, e.g. a cylindrical tube, the nuts having acorresponding cylindrical circumference and fitting slidably within thecylindrical tube.

[0005] At their ends, the nuts may have an actuating member which cantake several forms, dependant on the envisaged application of theactuator.

[0006] At or near the ends of the nuts facing away from each other aseal, e.g. a sealing bellows is provided, which seals are connected tothe respective ends of the cylindrical tube. The internally locatedscrew thread of nuts and screws is thereby well protected against dirt,etcetera. This is particularly of importance in the case of ball orroller screws.

[0007] The drive means are drivable through an opening in the housingand can be carried out as a spline, e.g. a screw gear wheel.Furthermore, the drive means may comprise a motor, the stator of whichengages the housing, and the rotor of which is drivingly connected tothe spline.

[0008] According to a preferred embodiment, the motor is drivablyconnected to a drive gear wheel which meshes with the spline, said drivegear wheel being of greater width than the spline so as to allow axialdisplacements of the screws and spline while maintaing the mesh.

[0009] As a result, the nuts which are driven towards or away from eachother can adapt themselves freely to the surrounding structure throughthe actuating heads thereof.

[0010] The maximum diameter of the spline is smaller than the diameterof the bore of the cylindrical tube, the nuts at their side facing thespline being recessed so as to allow displacement of said nuts alongsaid drive gear wheel.

[0011] The housing and the nuts can be held non-rotatably with respectto each other through a groove-pin connection.

[0012] The invention is furthermore related to an arrangement for for adrum brake, comprising a backing plate to be connected to a vehiclewheel suspension, e.g. a steering knuckle, housing etc., a pair of brakeshoes supported on said backing plate, a screw actuator engaging saidbrake shoes and a motor for driving said screw actuator so as to obtaina linear movement thereof for displacing the brake shoes outwardly andaway from each other vice versa, said actuator comprising a housing anda screw mechanism which is supported with respect to the housing, andwith at least one screw and a nut.

[0013] Such arrangement is known from U.S. Pat. No. 5,310,026 as well.

[0014] According to the invention, the screw mechanism comprises twoaxially aligned screws which have opposite lead angles and twocorresponding nuts, said screws each engaging a respective nut the drivemeans being connected to both screws or to both nuts.

[0015] The actuating members may, according to a first possibility, beconnected pivotably to a respective brake shoe. Alternatively, eachactuating member may have an abutment surface, the brake shoes beingheld under pretension against a respective abutment surface by means ofa spring.

[0016] In the latter case, each nut is held non-rotatably in thecylindrical tube. In case of a pivotable connection between actuatingmembers and brake shoes, no further precautions are necessary forpreventing mutual rotations of the nuts with respect to the housing.

[0017] The housing can be fixedly connected to the backing plate.

[0018] The invention is further related to an arrangement for a drumbrake, comprising a backing plate to be connected to a vehicle wheelsuspension, e.g. a steering knuckle, housing etc., a pair of brake shoessupported on said backing plate, a screw actuator engaging said brakeshoes and a motor for driving said screw actuator so as to obtain alinear movement thereof for displacing the brake shoes outwardly andaway from each other, said actuator comprising a housing and a screwmechanism which is supported with respect to the housing, and twoaxially aligned screws which have opposite lead angles and twocorresponding nuts, said screws each engaging a respective nut, thedrive means being connected to both screws or to both nuts.

[0019] Such arrangement is known from U.S. Pat. No. 1,928,750 as well.According to the invention the nuts are axially slidable andnon-rotatable within the housing.

[0020] According to a preferred embodiment, the motor is drivablyconnected to a drive gear wheel which meshes with the spline, said drivegear wheel being of greater width than the spline so as to allow axialdisplacements of the screws and spline while maintaing the mesh.

[0021] As a result, the nuts which are driven towards or away from eachother can adapt themselves freely to the surrounding structure throughthe actuating heads thereof.

[0022] The maximum diameter of the spline is smaller than the diameterof the bore of the cylindrical tube, the nuts at their side facing thespline being recessed so as to allow displacement of said nuts alongsaid drive gear wheel.

[0023] The housing and the nuts can be held non-rotatably with respectto each other through a groove-pin connection.

[0024] The invention is furthermore related to an arrangement for for adrum brake, comprising a backing plate to be connected to a vehiclewheel suspension, e.g. a steering knuckle, housing etc., a pair of brakeshoes supported on said backing plate, a screw actuator engaging saidbrake shoes and a motor for driving said screw actuator so as to obtaina linear movement thereof for displacing the brake shoes outwardly andaway from each other vice versa, said actuator comprising a housing anda screw mechanism which is supported with respect to the housing, andwith at least one screw and a nut.

[0025] Such arrangement is known from U.S. Pat. No. 5,310,026 as well.

[0026] According to the invention, the screw mechanism comprises twoaxially aligned screws which have opposite lead angles and twocorresponding nuts, said screws each engaging a respective nut the drivemeans being connected to both screws or to both nuts.

[0027] The actuating members may, according to a first possibility, beconnected pivotably to a respective brake shoe. Alternatively, eachactuating member may have an abutment surface, the brake shoes beingheld under pretension against a respective abutment surface by means ofa spring.

[0028] In the latter case, each nut is held non-rotatably in thecylindrical tube. In case of a pivotable connection between actuatingmembers and brake shoes, no further precautions are necessary forpreventing mutual rotations of the nuts with respect to the housing.

[0029] The housing can be fixedly connected to the backing plate.

[0030] The drive means may comprise a magnet coupling for holding thebraking torque under currentless condition (hand brake).

[0031] The invention will now be described further with reference to adrum brake with an actuator according to the invention shown in thedrawings.

[0032]FIG. 1 shows a view on the arrangement according to the inventionincluding the actuator.

[0033]FIG. 2 shows a cross section to the arrangement according to FIG.1, including part of a brake drum.

[0034]FIG. 3 shows a first embodiment of the actuator according to theinvention.

[0035]FIGS. 4 and 5 show a second embodiment of the actuator.

[0036]FIG. 6 shows the actuator according to FIGS. 4 and 5 incombination with the drive motor.

[0037] The arrangement shown in FIGS. 1 and 2 comprises a backing plate19, which can be connected to a vehicle wheel suspension (not shown).Onto the backing plate, a pair of brake shoes 20, 21 is mounted. Saidbrake shoes 20, 21 are each supported on an anchor 28 of the backingplate 19. Through springs 26, 29, the brake shoes 20, 21 are constantlyurged towards the anchor 28, as well as to the screw mechanism 2.

[0038] Said screw mechanism 2, which is contained in a housing 1 whichis fixedly connected to the backing plate 19 as well, comprises twoaxially aligned screws 3, 6 which have opposite lead angles, as well astwo corresponding nuts 4, 7. The nuts 4, 7 are slidably, but nonrotatably through spline/groove connection 27, within the housing 1. Thescrews 2, 3 and nuts 4, 7 engage each other through balls 30 (ballscrews).

[0039] The nuts 4, 7 each carry an actuating head 8, 9, against thesurfaces 24, 25 of which the noses 31, 32 of the brake shoes 20, 21 areurged through spring 26.

[0040] Between the screws 3, 6, a spline wheel 5 is connected. As shownin the enlarged detail of FIG. 6, this spline wheel 5 protrudes throughan opening 12 in the housing 1. In this opening 12, a drive gear wheel16 is accommodated, the width of which is greater than the width of thespline 5. In turn, the gear wheel 16 engages the pinion wheel 33 whichis connected to the rotor 15 of the motor 13. This motor 13 is connectedto the backing plate 19 as well, however to the side opposite the sidewhere the actuator 1, 2 is mounted. The drive gear wheel thus protrudesthrough the opening 34 in the backing plate 19, as well as through theopening 12 in the housing 1. Upon energising the stator 14 of the motor13, the rotor 15, and thereby the pinion gear 33, the drive gear wheel16 and the spline 5 are set in rotation. Thus, the actuator and inparticular the screw mechanism 2, provides the desired mutualdisplacement of the braking shoes 20, 21 towards or away from the brakedrum 35 (shown in FIG. 2).

[0041] In the embodiment of FIGS. 1, 2 and 3, the nuts 4, 7 each carryan actuating member 8, 9 having a flat outer surface 24, 25. Asmentioned, in that case it is necessary to prevent rotation of the nuts4, 7 with respect to the housing 1 by means of the spline/grooveconnections 27.

[0042] In the embodiment of FIGS. 4, 5, and also of FIG. 6, theactuating members are carried out with flanges 36, 37 having eyes 22,23. The corresponding ends 31, 32 of the brake shoes 20, 21 in that casecarry eyes as well, in such a way that the pivotable connection isobtained by inserting pins through the respective eyes 22, 23, as wellas the eyes in the ends 31, 32 (not shown) of the brake shoes 20, 21.

[0043] In this embodiment, the nuts 4, 7 are held against rotationthrough this pivotable connection, so that no additional spline/grooveconnection is necessary here.

[0044] By means of bellows 10, 11, the interior of the housing 1 isprotected against dirt etcetera.

1. Actuator for a drum brake, comprising a housing (1), a screwmechanism (2) comprising two axially aligned screws (3, 6) which haveopposite lead angles and two corresponding nuts (4, 7), said screws (3,6) each engaging a respective nut (4, 7), which screw mechanism issupported with respect to the housing (1), and drive means (5) forproviding a linear movement of at least one of the screw (3) and nut (4)with respect to the housing (1) upon driving the screw mechanism (2),characterized in that the nuts (4, 7) are axially slidable andnon-rotatable within the housing (1).
 1. Actuator for a drum brake,comprising a housing (1), a screw mechanism (2) comprising at least onescrew (3) and a nut (4), which screw mechanism is supported with respectto the housing (1), and drive means (5) which are drivingly connected tothe screw mechanism (2) for providing a linear movement of at least oneof the screw (3) and nut (4) with respect to the housing (1) upondriving the screw mechanism (2), characterized in that the screwmechanism (2) comprises two axially aligned screws (3, 6) which haveopposite lead angles and two corresponding nuts (4, 7), said screws (3,6) each engaging a respective nut (4, 7), the drive means (5) beingconnected to both screws (3, 6) or to both nuts (4, 7).
 2. Actuatoraccording to claim 1, wherein the housing comprises a cylindrical tube(1), the nuts (4, 7) having a corresponding cylindrical circumferenceand fitting slidably within the cylindrical tube (1).
 3. Actuatoraccording to claim 2, wherein the nuts (4, 7) at their ends facing awayfrom each other have an actuating member (8, 9).
 4. Actuator accordingto claims 2 or 3, wherein at or near the ends of the nuts (4, 7) facingaway from each other a seal, e.g. a sealing bellows (10, 11) isprovided, which seals are connected to the respective ends of thecylindrical tube (1).
 5. Actuator according to claims 2, 3 or 4, whereinthe drive means comprise a disc (5) which is drivable through an opening(12) in the cylindrical tube (1).
 6. Actuator according to claim 5,wherein the drive means comprise a spline (5), e.g. a screw gear wheel(5).
 7. Actuator according to claim 6, wherein the drive means comprisea motor (13), the stator (14) of which engages the housing (1), and therotor (15) of which is drivingly connected to the spline (5). 8.Actuator according to claim 7, wherein the rotor (15) is drivablyconnected to a drive (16) gear wheel which meshes with the spline (5),said drive gear wheel (16) being of greater width than the spline (5) soas to allow axial displacements of the screws (3; 6) and spline (5)wheel while maintaing the mesh.
 9. Actuator according to claim 8,wherein the maximum diameter of the spline (5) is smaller than thediameter of the bore (17) of the cylindrical tube (1), and the nuts (4,7) at their side facing the spline (5) being recessed (18) so as toallow displacement of said nuts (4, 7) along said drive gear wheel (5).10. Actuator according to any of the preceding claims, wherein the screwmechanism (2) comprises ball or roller screws.
 11. Actuator according toany of claims 1-10, wherein the housing (1) and a nut (4) are heldnon-rotatably with respect to each other through a groove-pin connection(27).
 12. Actuator according to any of claims 1-11, wherein an encodersensor is provided for measuring rotations and/or linear displacements.13. Actuator according to any of the preceding claims, wherein at leastone component is obtained by means of hard-turning.
 14. Actuatoraccording to any of the preceding claims, wherein at least one componentis obtained by means of powder metallurgy.
 15. Arrangement for a drumbrake, comprising a backing plate (19) to be connected to a vehiclewheel suspension, e.g. a steering knuckle, housing etc., a pair of brakeshoes (20, 21) supported on said backing plate (19), a screw actuatorengaging said brake shoes and a motor (13) for driving said screwactuator (1, 2) so as to obtain a linear movement thereof for displacingthe brake shoes (20, 21) outwardly and away from each other, saidactuator comprising a housing (1) and a screw mechanism (2) which issupported with respect to the housing (1), and with at least one screw(3, 6) and a nut (4, 7), characterized in that the screw mechanism (2)comprises two axially
 15. Arrangement for a drum brake, comprising abacking plate (19) to be connected to a vehicle wheel suspension, e.g. asteering knuckle, housing etc., a pair of brake shoes (20, 21) supportedon said backing plate (19), a screw actuator engaging said brake shoesand a motor (13) for driving said screw actuator (1, 2) so as to obtaina linear movement thereof for displacing the brake shoes (20, 21)outwardly and away from each other, said actuator comprising a housing(1) and a screw mechanism (2) which is supported with respect to thehousing (1), and two axially aligned screws (3, 6) which have oppositelead angles and two corresponding nuts (4, 7), said screws (3, 6) eachengaging a respective nut (4, 7), the drive means (5) being connected toboth screws (3, 6) or to both nuts (4, 7), characterized in that thenuts (4, 7) are axially slidable and non-rotatable within the housing(1). aligned screws (3, 6) which have opposite lead angles and twocorresponding nuts (4, 7), said screws (3, 6) each engaging a respectivenut (4, 7) the drive means (5) being connected to both screws (3, 6) orto both nuts (4, 7).
 16. Arrangement according to claim 15, wherein thehousing comprises a cylindrical tube (1), the nuts (4, 7) having acorresponding cylindrical circumference and fitting slidably within thecylindrical tube (1).
 17. Arrangement according to claim 16, wherein thenuts (4, 7) at their ends facing away from each other have an actuatingmember (8, 9).
 18. Arrangement according to claim 17, wherein eachactuating member (8, 9) is connected pivotably (22, 23) to a respectivebrake shoe (20, 21).
 19. Arrangement according to claim 17, wherein eachactuating member (8, 9) has an abutment surface (24, 25), the brakeshoes being held under pretension against a respective abutment surface(24, 25) by means of a spring (26).
 20. Arrangement according to claim19, wherein each nut (4, 7) is held non-rotatably in the cylindricaltube (1).
 21. Arrangement according to claim 20, wherein at or near theends of the nuts (4, 7) facing away from each other a seal, e.g. asealing bellows (10, 11) is provided which seals are connected to therespective ends of the cylindrical tube (1).
 22. Arrangement accordingto claim 21, wherein the drive means comprise a spline (5) which isdrivable through an opening (12) in the cylindrical tube (1). 23.Arrangement according to claim 22, wherein the drive means comprise ascrew gear wheel (5).
 24. Arrangement according to claim 23, wherein thedrive means comprise a motor (13), the stator (14) of which engages thehousing (1), and the rotor (15) of which being drivingly connected tothe screw gear wheel (5).
 25. Arrangement according to claim 24, whereinthe rotor (15) is drivable connected to a drive (16) gear wheel whichmeshes with the screw gear wheel (5), said drive gear wheel (16) beingof greater width than the screw gear wheel (5) so as to allow axialdisplacements of the screws (3; 6) and screw gear (5) wheel whilemaintaing the mesh between those gear wheels (5, 16).
 26. Arrangementaccording to claim 25, wherein the maximum diameter of the screw gearwheel (5) is smaller than the diameter of the bore (17) of thecylindrical tube (1), and the nuts (4, 7) at their side facing the drivegear wheel (5) being recessed (18) so as to allow displacement of saidnuts (4, 7) along said drive gear wheel (5).
 27. Arrangement accordingto any of claims 15-26 wherein the screw mechanism (2) comprises balland/or roller screws.
 28. Arrangement according to any of claims 15-27,wherein the housing (1) is connected to the backing plate (19). 29.Arrangement according to any of claims 15-28, wherein the drive comprisea magnet coupling for holding the braking torque under currentlesscondition (hand brake).